Monday, November 28, 2016

CDC FluView Week 46: 1 Novel H1N2v Infection In Iowa


Last week's FluView report was delayed until today due to the Thanksgiving Holiday. For the most part, influenza activity remains low in the United States and H3N2 remains the most commonly reported influenza strain reported this fall.

The CDC does report, however, on the detection of the 23rd novel swine variant infection of 2016, involving the H1N2v virus in a patient in Iowa. 

Reports of human infection with novel swine variant influenza (H1N1v, H1N2v & H3N2v) are fairly rare, due to their (often) unremarkable presentation and limited laboratory testing, but likely occur more often than we know.

The H3N2v strain is by far the most common, making up 94% of all reported cases (n=372) in the United States over the past 11 years.  H1N1v comes in 2nd, with 20 cases (4%).

H1N2v is the least common, with just 8 cases reported (the last one was in Wisconsin last June) up until today.

Today's case - the 9th since 2005 - is described by the FluView as:

Novel Influenza A Virus:

One human infection with a novel influenza A virus was reported by the state of Iowa. The person was infected with an influenza A (H1N2) variant (H1N2v) virus. The patient was not hospitalized, and has fully recovered from their illness. No human-to-human transmission has been identified and the case reported close contact with swine in the week prior to illness onset.
Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully appreciated and appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza infection in humans, and strategies to interact safely with swine can be found at

While we’ve not seen sustained or efficient spread of these swine variant viruses in humans - like all flu viruses - swine variant viruses are capable of evolving, reassorting, and adapting to their hosts.

Since the influenza subtypes that commonly circulate in swine (H1, H2 & H3) are also the same that have caused all of the human pandemics going back 130 years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?), they are generally regarded as having less far to `jump’ to humans than many avian viruses.

Which is precisely how the H1N1 pandemic virus emerged in 2009, after kicking around (and reassorting in) swine herds for a decade or longer.

Last October, in MMWR: Investigation Into H3N2v Outbreak In Ohio & Michigan - Summer 2016,  we looked at the CDC's investigation into a cluster of 18 H3N2v cases across two states during the month of August. This was the biggest outbreak of swine variant infections we'd seen since 2012, when more than 300 cases were reported across 10 states. 
The `headline' in that report was that 16 of the 18 cases analyzed belonged to a new genotype not previously detected in humans. 

As with avian influenza, swine flu viruses are constantly evolving, which is why we watch reports like today's with particular interest. For more on swine variant viruses, both in the United States and around the world, you may wish to revisit:

PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza
Front. Microbiol.: A Novel H1N2 Reassorted Influenza Virus In Chinese Pigs
Sci Rpts: Transmission & Pathogenicity Of Novel Swine Flu Reassortant Viruses
Eurosurveillance: Seroprevalence Of Cross-Reactive Antibodies To Swine H3N2v – Germany

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